#include <stdio.h>

int main()
{
    int n, i;
    double sum = 0, fact = 1;
    scanf("%d", &n);
    for (i = 2; i <= n * 2; i += 2)
    {
        fact = fact / (i - 1) / i;
        sum += fact;
    }
    printf("%.6lf\n", sum);
    return 0;
}
